1. Field of the Invention
The present invention relates to an edge rinse after resist is coated on a substrate, and particularly to an apparatus (edge rinse apparatus) for removing resist coated on a peripheral portion of a principal surface of a substrate, an end surface of the substrate, and a rear surface of the substrate, and a method (edge rinse method) of removing the resist. In the present specification, every apparatus having the function of making the edge rinse is called the edge rinse apparatus.
2. Description of the Related Art
In various fields, a pattern is formed on a substrate by a lithography technique using resist. Particularly, this is an inevitable technique when an element using semiconductor, for example, a thin film transistor (hereinafter referred to as a TFT) is fabricated.
The lithography technique is used for fabrication of a display device using a glass substrate, for example, a liquid crystal display device, a plasma display panel (PDP), an EL (Electroluminescence) display device, an FED (Field Emission Display), etc., or fabrication of an image sensor using a CCD, CMOS, etc. In the present specification, the resist indicates a positive resist which comes to have solubility to a developing solution when light (visible light or ultraviolet rays) or X-rays are irradiated.
As a coating method of resist, a rotation coating method using a spin coater is generally used. That is, after the resist is dropped onto the principal surface of a substrate, the substrate is rotated, so that the resist is applied by generated centrifugal force to form a coating film of uniform thickness. However, since the resist rounds to the end surface of the substrate and the rear surface of the substrate at the same time, it is coated on not only the principal surface of the substrate but also the end surface of the substrate and the rear surface of the substrate. In order to prevent raising dust and pollution to a conveyance system, etc., it has been necessary to make a removal of the resist coated on the peripheral portion of the principal surface of the substrate, the end surface of the substrate, and the rear surface of the substrate (hereinafter, they are together referred to as an unnecessary portion), a so-called edge rinse. In the present specification, the principal surface of the substrate means a surface having an object to be processed on which a pattern is formed.
As a method of the edge rinse, there are known a method of rotating a substrate while a washing solution is discharged to the rear surface of the substrate, and a method of moving a recess portion for discharging a washing solution to an unnecessary portion and a washing nozzle having the function of sucking and removing a dissolved resist or the like. Here, as the washing solution, a solution which easily dissolves the resist is used. However, these methods have problems as set forth below.
First, the state of a substrate after processed by the conventional edge rinse method is shown in FIG. 9. In FIG. 9, a resist 902 exists on a substrate 901, and a resist on an unnecessary portion, that is, a substrate principal surface peripheral portion 903, a substrate end surface 904, and a substrate rear surface 905 is removed. Here, although the resist coated on the unnecessary portion is dissolved and removed by a washing solution, since the resist dissolved by the washing solution is accumulated at an end 906 of the resist, a swelling of the resist is produced as shown in FIG. 9.
Since the resist is hardened or its quality is changed through baking and doping steps, it becomes difficult to remove this swelling by ashing, and a resist residue is liable to be produced at the end of the substrate. Then, the yield is lowered by raising dust due to peeling of the resist residue, or a step of removing the resist residue becomes necessary. Further, in this swelling, when exposure or ion implantation is carried out, foaming is liable to occur by gas generated in the resist film, and wastes due to a cause different from the foregoing raising dust are also produced.
Besides, since a wet etching by a washing solution is made as a base, it is difficult to uniformly control the distance from the substrate end of the substrate principal surface peripheral portion, and the resist end has been irregular. Besides, the washing solution rebounds on a cup and is splashed on a necessary portion (region where a pattern is formed), so that the resist of the necessary portion is partially dissolved and poor pattern formation occurs.